1. Field of the Invention
This invention relates to electrical electrodes and, more particularly, to a cardiac lead assembly and a method of attaching a cardiac lead assembly to a patient's heart.
2. Prior Art
For some time, electrical leads have been used to conduct pacing signals from a pacemaker to the heart of a living subject. Such cardiac electrodes typically terminate in an electrode tip which must be surgically implanted in the heart to deliver the desired pacing signals to an appropriate portion of the heart. Screw-in electrodes can be implanted in the heart with relatively little trauma to the heart muscle. However, even with screw-in electrodes, accurate manual implantation can be difficult due to movement of the heart, and this movement can result in undesired laceration of the heart by the electrode before the electrode has become embedded in the heart.
Lacerations of the type described above can result in the formation of undesirable scar tissue near or immediately adjacent to the electrode. Such scar tissue tends to increase the voltage of the pacing signal required to pace the heart properly. This increased voltage in turn reduces the life of batteries used to power the associated pacemaker.
In addition, many commonly used screw-in electrodes use perforated, fabric skirts near the screw-in electrode as an aid in fastening the electrode to the heart. In use, these fabric skirts serve as bonding sites at which heart tissues can engage the electrode to hold the electrode firmly to the heart. Such bonding skirts present important disadvantages in that they do not significantly help to secure the electrode to the heart for some period of time after the electrode has been implanted in the heart. This is because heart tissues do not grow into and around the fabric skirt until a period of time ranging from several days to weeks has elapsed. During this period of time, prior to the attachment of the skirt to the heart, it is the screw-in electrode itself which holds the electrode in place.
Once fabric skirts of the type described above have become embedded in heart tissue, the electrode often cannot be removed from the heart without cutting the skirt and associated heart tissue from the heart. Thus, the removal of the electrode is a surgical procedure which serves further to traumatize the heart and can result in the formation of additional scar tissue.
Many conventional screw-in electrodes have electrodes approximately six millimeters in length. However, it has been established that the wall thickness of the muscle layer of the apex of the left ventricle of many human subjects is at its thinnest point less than two millimeters in thickness. Thus, there is a very real danger that screw-in electrodes of the conventional type may perforate the ventricular wall.
U.S. Pat. No. 4,452,254 to Goldberg et al. discloses a cardiac lead assembly with an elongatable coil spring which serves to connect a screw-in electrode tip with a connector. A surgeon uses the coil spring to first stretch and then release the coil to snap forward the electrode tip at the heart of a patient to penetrate the surface of the heart. Goldberg et al. discloses that this type of slingshot method preferably also imparts an angular momentum to the electrode tip. Other types of pacing leads include active fixation leads such as with pronged tips and endocardial pinch-on tips, and passive fixation leads such as with helical coil tips, tined tips, balloon tips and porous tips.
One major problem with devices known in the prior art is that angular motion or rotation of an electrode tip, such as a screw-in tip, is generally provided through the use of a stylet, which is manually turned by a surgeon, or by manually rotating the lead conductor with the lead body. This method and the slingshot method disclosed in Goldberg et al. do not provide an automatic and reliably controllable angular rotation of a tip for attachment to a patient's heart in a relatively quick manner and with relatively little trauma to the heart.
It is therefore an objective of the present invention to provide an improved cardiac lead assembly and method of attaching the same that overcomes disadvantages in the prior art devices as well as provide other advantages.